1. Field of the Invention
The present invention relates to locomotive braking systems and, more particularly, to a system and method for applying safety override braking, referred to as penalty braking, in response to a request from an external safety system.
2. Description of the Related Art
Locomotive air brake systems control the brakes of the train by modulating the pressure in a compressed air pipe, called the “brake pipe,” which runs continuously through the entire train. The brake pipe must be supplied with compressed air from the locomotive main supply reservoirs in order to release the train brakes, and reducing the pressure in the brake pipe causes the train brakes to apply. The air brake system allows the user to control the flow of compressed air into and out of the brake pipe to apply and release the train brakes. Some newer locomotive air brake control systems equipped with Electronically Controlled Pneumatic (ECP) brakes may alternately control the train braking level via electronically-generated commands that are distributed via electronic messaging communication throughout the train. Whether conventional brake pipe modulation or ECP control is used, the air brake system may also be configured to respond to an external safety system by applying the train brakes without any operator action. This automatic brake application is commonly referred to as penalty braking.
Current locomotive braking systems, whether electronic or pneumatic, generally emulate the function of pneumatic brake systems with respect to penalty braking. In these systems, the brake system responds to an electrical or pneumatic signal from the external safety system by reducing the brake pipe pressure to zero or to a fixed value. The brake system may also be configured to provide signals to the locomotive traction control system that indicates that the penalty brakes have been applied, so that power to the traction system and the dynamic brake system can be inhibited. In conventional locomotive braking systems equipped with penalty braking, the amount of braking that is triggered is static and constitutes a predetermined level of braking, which may even be the maximum brake application that is possible. Accordingly, there is a need in the art for a system that can apply an appropriate and varying amount of penalty braking in response to an external safety system.